Apple Watch 4 - ‘Set Up Mobile’ Error

I’ve been trying without sucess to pair my Apple Watch 4 to my iPhone 6. The error I receive is:

“This service needs an update to use Telstra One Number”

After a couple of long web chats and a store visit (web chat support told me to go there) no luck.

- iOS up to date (12.1.2)- watchOS up to date (5.1.2)- Telstra One Number subscription is active (confirmed in-store)

But still the error. The error page is Telstra branded and says that a fix is required at the Telstra end.

So besides any help with the error does anyone have any suggestions on how to get this solved or escalated? The web chat and in-store staff were mostly helpful, but I’ve obviously capped out their expertise. Four different people looked at this when I went in a couple of days ago.